FILTER MEDIA TREATMENT OF A FLUID FLOW TO REMOVE COLLOIDAL MATTER

Abstract: Colloidal matter is removed from a fluid flow (122) by first adsorbing a coagulant (162) onto the surface of a finely divided filter media (126), and thereafter passing a colloid-containing fluid (122) through the filter media (126). The adsorbing of coagulant (162) is accomplished with the filter media (126) off-line, and it is returned on-line for filtering of the fluid. After the coagulant (162) is adsorbed onto the filter media (126), it is not necessary to continue feeding coagulant during on-line operation, as the adsorbed coagulant captures the colloidal matter in the fluid (122) and retains it on the surface of the filter media (126). The captured colloidal matter is removed during back washing of the filter media (126).

Description: FILTER MEDIA TREATMENT OF A FLUID FLOW TO REMOVE COLLOIDAL MATTER BACKGROUND OF THE INVENTION Fluid flows often contain solid and soluble contaminants that must be removed before discharge or reuse of the fluid. In one common cleaning approach, during on-line operation the contaminated fluid is passed through a media filter containing a packed, finely divided filter media material such as crushed coal, sand, and gravel. The large particles in the fluid flow are captured within the filter media, for later removal by off-line backflushing. The colloidal particles are not readily captured by the filter media, because they are so small that they pass through the passageways within the filter media. To permit capture of the colloidal particles, it is a common, but not universal, practice to add a small amount (typically about 2-20 parts per million) of a coagulant to the fluid flow, upstream of the media filter. The coagulant causes the colloidal particles to coalesce together into larger particles, which can be captured within the media filter. Such systems work well in an idealized operation, where precisely the right amount of coagulant is added upstream of the media filter. However, in actual practice problems can arise if exactly the right amount of coagulant is not added. If too little coagulant is added, some of the colloidal matter is not captured. If too much coagulant is added, the coagulant reacts with the anti-sealant compound to form a thick, sludge-like residue that can foul the downstream portion of the system. It is difficult to know precisely the amount of coagulant to add, because the water quality and fluid flow rate can vary over time. As a result of the risk of fouling due to the reaction of excess coagulant and anti-sealant compound, most fluid-treatment plants of this type operate with no coagulant addition at all, or a deficiency of coagulant addition as compared with the optimal value for removing all of the colloidal material. SUMMARY OF THE INVENTION In accordance with the invention, a method of purifying a fluid flow comprises the steps of providing a coagulant compound in a form that can adsorb onto the surface of a filter media and providing in a media filter a finely divided solid filter media that can adsorb the coagulant compound at its surface. The filter media is treated with the coagulant compound form such that a quantity of the coagulant compound is bound onto the surface of the filter media, in off-line treatment of the media filter. Preferably, the coagulant is of a stable, nontoxic type. The method further includes providing a flow of a fluid containing colloidal matter, and passing the fluid through the filter media, in on-line operation of the media filter. In the preferred approach, there is no further or continuous addition of coagulant to the fluid flow when the media filter is on-line to filter the fluid containing the colloidal matter. Thus, there can be no addition of the coagulant in too-large or too-small a quantity, and the method is self regulating in this respect. The invention also extends to the preparation of a dry filter media material that is suitable for loading into media filters for specialized applications. Thus, a dry filter media material comprises a finely divided filter media, and a coagulant compound bound by adsorption at the surface of the filter media. The approach of the invention achieves optimal, self-regulated removal of colloidal matter from the fluid, as well as the removal of larger particles through the use of a filter media. The consumption of expensive coagulant chemicals is reduced. Adverse reactions with anti-sealants due to overdoses of coagulant are avoided. The system of the invention can therefore be readily operated by unskilled operators. The fluid which has been processed to remove solids can thereafter be treated by reverse osmosis or other technique to remove soluble impurities. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of a filtration system according to the invention, with an enlarged insert showing a filter media particle; Figure 2 is a process flow diagram of one embodiment of the invention; and Figure 3 is a process flow diagram of another embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a system 120 according to the invention, and Figure 2 depicts the process steps associated with this system 120. An input fluid flow 122 is introduced into a media filter 124, which contains a bed of particles of a filter media 126. (As used herein, the "filter media" is a finely divided solid material which accomplishes filtration. In its normal use, it is contained within the "media filter" container.) Each filter media particle 128, also shown in a magnified view in Figure 1, comprises a substrate 160 and a bound (adsorbed) layer 162 of a coagulant compound. A preferred procedure for forming the adsorbed layer 162 on the particle substrate 160, to produce the particle 128, is shown in Figure 2. A filter media substrate 160 Is first provided, numeral 60. The particle 160 may be of any type operable to adsorb the selected coagulant. Naturally occurring silica-based materials such as rocks, sand, and gravel have been found to adsorb conventional coagulants in varying degrees. Carbon-based materials such as crushed coal and granular activated carbon can also adsorb coagulants. Other naturally occurring and synthetically prepared materials such as glass have been found to have only a very small adsorbing capability, and are not normally good candidate materials for this application. However, such materials of limited adsorbing capability may be surface treated to improve their performance as substrate materials. For example, glass beads may be rendered suitable for the present process by coating the beads with a binding agent such as polyaerylic acid and drying the beads. It is believed that the polyaerylic acid supplies electronegative groups on the surface of the glass beads to which the positively charged groups of the coagulant can bond. Any treatment which produces a suitably prepared surface on otherwise unsuitable candidate substrate materials would be operable. Other operable binding agents such as other acrylics, epoxies, phenolics, sulfonated plastics, polyurethanes , silanes, ion exchange resins, and nylons can be used, or the substrate beads can be made in their entirety from such materials. After this surface treatment, the beads are then treated with coagulant compound, as next described, and used in the process. The most successful naturally occurring filter media particle substrates 160 have been found to be carbon-chain materials, such as organic polymeric materials and others that may include additional atoms wherein carbon atoms are linked together by carbon-carbon bonds. Materials used as ion exchange resins have been found to be suitable, as they adsorb the coagulants well and have a high surface area due to their mode of manufacture. The most effective ion exchange particle materials are cation exchange resins, with weak acid cation exchange resins such as methacrylate-divinyl- benzene resins (such as Rohm and Haas DP-1 resin) being preferred to strong acid cation exchange resins. Further, it is preferred that the ion exchange resin be in the spent (e.g., with sodium replaced by calcium and magnesium) form prior to adsorption of the coagulant. Other suitable filter media materials include metals such as aluminum, steel, stainless steel, and copper; and ceramics such as porcelain, cement, fused alumina, and silicon carbide. The filter media can also be made of new materials designed for enhanced operation when used in conjunction with the present invention. For example, it is desirable to have an inexpensive, noncorroding filter media material which has a relatively heavy weight to prevent loss of media during backwashing. The filter media may be made of plastics having metal particles mixed therewith ("filled plastics") or weighted plastic filter media that are formed as hollow plastic shells with a dense metal weight within the interior hollow region. A coagulant compound Is provided, numeral 62, in a form that can adsorb onto the surface of the filter media substrate particles 160. The coagulant compound must be stable in the fluid being processed and must be nontoxic and environmentally acceptable. No functionality limitation on the type of coagulant compound has been found, and all types tested have been found operable. However, as will be discussed, some operable coagulant compounds are not preferred for use because they are unstable and/or potentially toxic or environmentally damaging. The preferred coagulant compounds include poly(diallyl-dimethyl ammonium chloride) (DADMAC) type coagulants, such as Magnifloc 591C available commercially from American Cyanamid and as Filtermate 150 available commercially from Argo Scientific, and poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride having a molecular weight of about 2500 and available commercially as Mayosperse 60 from The Mayo Corporation. The latter compound is most preferred because it is also a biocide that inhibits biological growth in the system. Examples of other operable coagulant compounds include poly( 2-hydroxy-propyl-N,N-dimethyl ammonium chlorides ("EPi/DMA polymers") and quaternized polyamines such as poly[oxyethylene- (dimethyl-iminid ) ethylene(dimethyliminio ) ethylene dichloride. Although functionally operable to effect the coagulation, polyamine coagulants are less preferred due to their instability. The members of one class of polyamines are not to be used for presently known applications due to their potential toxicity. The charge density of polyamines as a group is affected by the pH of the fluid contacting the coagulant. Most polyamines are sensitive to degradation by contact with chlorine. One unique class of polyamines encompasses the non-quaternized polyamines such as formaldehyde-melamine polymers. Melamine formaldehyde coagulant in particular has the further disadvantage that commercial formulations may contain low residual contaminations of formaldehyde, a toxic material. This class of coagulants would therefore not be suitable for removing particulate from water, foods and beverages, or other substances that might enter the human food chain. To summarize, most polyamine coagulants may functionally be used in some situations but are not preferred because of their instability by virtue of pH dependence and chlorine sensitivity. Melamine formaldehyde polyamine is not to be used in any presently known application because of its potential toxicity. The filter media substrate particles 160 are treated with the selected coagulant compound to adsorb the layer 162 onto the surface of each particle 160, see numeral 64 of Figure 2. The treatment can utilize a batch approach wherein the coagulant compound is introduced into the media filter 124 and allowed to remain for a period of time. More preferably, the treatment 64 is accomplished by a flow approach with the media filter 124 off-line. "Off-line" means that there is no input fluid flow 122 through the media filter 124. In one approach to the treatment 64 , the media filter 124 is taken off line by closing a valve 134 and a valve 136 to isolate the media filter 124. Adsorption is accomplished by opening valves 164 and 166 to permit a flow of the liquid coagulant from a source 132 through the bed of filter media particles 160, for a period of time that is typically about 15 minutes. Preferably, the liquid coagulant is in a concentrated form, but may be slightly diluted without substantial interference with the adsorption process. The concentrated liquid coagulant adsorbs onto the surface of the particles 160 more rapidly than does a diluted coagulant. The excess unadsorbed coagulant can be discarded or returned to the source 132 for later reuse. In the latter case, there is typically some dilution, but the diluted coagulant from the source 132 can be reused until it can no longer achieve adsorption within an acceptable treatment time. In an alternative approach to the treatment 64, the coagulant compound is introduced into the process input fluid flow 122 for a period of time, usually about 15 minutes. During this period, the media filter outflow 150 is diverted to waste and not permitted to reach the RO unit 142 due to the high coagulant concentration. Thus, the media filter 124 remains off line during this treatment. Returning to the discussion of the preferred treatment 64, after the adsorption treatment is complete, the valves 164 and 166 are closed. The valves 134 and 136 are opened, bringing the media filter 124 back on line. The input fluid flow 22, numeral 66, resumes so that the fluid to be cleaned of particulate again flows through the filter media 126, numeral 68. No continuous flow of coagulant is added to the fluid flow 122 when the media filter 124 is on line in the preferred approach. The adsorbed coagulant on the filter media 126 accomplishes the removal of colloidal matter in the fluid flow. The fluid flow 150 leaving the media filter 124, clarified of large solid matter and small colloidal matter, may optionally be (and usually Is) further processed to remove dissolved matter, numeral 70. In the preferred approach, this processing is accomplished with a reverse-osmosis unit 142, to produce an output fluid flow 144 that is clarified of solid and dissolved matter. An anti-sealant flow 146 from a source 148 may be added to the fluid flow 150, after the fluid flow leaves the media filter 124 but before it enters the reverse-osmosis unit 142. The anti-sealant inhibits the development of scaling in the reverse-osmosis unit. A typical anti-sealant chemical is polyaerylic acid. The present approach achieves a major improvement over the prior approach in regard to the anti-sealant addition. In the prior approach a coagulant flow was added to the input fluid flow. If the coagulant flow rate at any moment was in excess of that required to agglomerate the colloidal matter concentration at that moment, some coagulant would pass through the media filter. This excess coagulant would react with the anti-sealant to produce a gummy residue in the reverse-osmosis unit. With the present approach, this problem is prevented because there is no continuous flow of coagulant. In most media filters, it is necessary to periodically backwash the filter media, numeral 72 of Figure 2, to remove accumulated solid matter. To accomplish the backwashing, the media filter 124 is taken off line by closing the valves 134 and 136. Backwash valves 138 and 140 are opened to permit a backwash flow to pass countercurrently through the filter media 126. After a sufficient time to remove accumulated solid matter, the valves 138 and 140 are closed and the valves 134 and 136 are opened to bring the media filter 124 back on line. Both the backwash step 72 and the treatment step 64 are accomplished with the media filter off line. In the preferred approach, the the backwash step and the treatment step to replenish the coagulant layer 162 are performed in the same off-line cycle. The steps 72 and 64 can be done simultaneously, so that the coagulant mixes with the backflow, or serially, with the backwash 72 preferably completed prior to starting the coagulant treatment 64. Or, as discussed for the alternative embodiment, the coagulant can be flowed through the media filter mixed with input fluid flow and with the media filter off line. After these steps 72 and 64 are completed, the media filter 124 is brought back on line and fluid treatment continues. The backwashing 72 and coagulant treatment 64 replenishing of the coagulant layer 162 permit the filter media material to be used in multiple cycles. In another aspect of the invention, a dry, solid, finely divided, particulate filter media can be prepared as shown in Figure 3. The filter media is provided, numeral 80 and the coagulant compound is provided, numeral 82. The filter media is treated to adsorb coagulant onto its surface, numeral 84. These steps 80, 82, and 84 are respectively identical to the steps 60, 62, and 64 of Figure 2, and that discussion is incorporated here. After the coagulant layer is formed on the surface of the filter media particles, the particles are dried, numeral 86, to produce a granular solid material. This material can be bagged or provided in bulk form to filter media users. It is a unique material, as no other filter media has an adsorbed coagulant layer. It can be used in systems which are not designed for backwash and regeneration processing. An example of such a system would be a water purification system that could be airlifted to a disaster area or battle area for quick response, without the weight associated with backwash and regeneration processing. The following examples are presented to illustrate aspects of the invention. They should not be interpreted as limiting the scope or operation of the invention in any respect. Example 1 Five candidate finely divided filter media materials were evaluated for their ability to adsorb coagulant. The candidate substrate materials were styrene-divinyl benzene sulfonic acid, a strong acid cation exchange resin available commercially as Dowex 51-XB; methacrylic acid-divinyl benzene, a weak acid cationic exchange resin available commercially as Rohm & Haas Amberlite DP-1; xytel nylon available commercially from Dupont; untreated soda-lime silica glass available commercially from Cataphote; and coal/sand/garnet mixed filter media. No pre-adsorption surface preparation of the filter media particles was done. Absorption testing was performed by shaking 10-25 cubic centimeters of the filter media substrate material in 50 millillters of a 100 ppm (parts per million) solution of the selected coagulant. The coagulant remaining in solution after the adsorption was measured with a Taylor polyquat test kit. The results were as follows, with each condition expressed as substrate material/coagulant, and coagulant adsorbed in 10 ~3 milligrams adsorbed per square centimeter of substrate (media) surface area: nylon/Filtermate 150, 12.3; nylon/Mayosperse 60, 0.05; Dowex/Mayosperse 60, 4.4; Amberlite/Mayosperse 60, 2.6; sand/Mayosperse 60, 2.2; coal/Mayosperse 60, 1.5; garnet/Mayosperse 60, 0.84; untreated glass/Mayosperse 60, 0.5; untreated glass/Filtermate 150, 0.45. Example 2 A sixth and seventh filter media material were prepared by first surface treating particulates in order to increase their adsorption of coagulant. The sixth filter media material was prepared by treating soda-lime silica glass beads to increase their adsorption of coagulant. The glass beads were first contacted to polyaerylic acid resin in the form of Liquitec Acrylic gel medium available from Binney & Smith, Easton, PA. The glass beads were contacted to the polyaerylic acid resin and dried in a drum mixer for 12 hours. The treatment was repeated to apply a second coating of the polyaerylic acid resin to the glass beads. After each treatment, most of the glass beads remained free flowing, but there was some lumping of glass beads together. The lumps, where present, could be easily broken up by hand. The treated glass beads of the sixth filter media material were studied microscopically, and were observed to have irregular coatings of the polyacrylic acid resin. Further process development of the coating procedure is expected to improve the coating regularity and thence the performance of the sixth filter media material. To prepare a seventh filter media material, the surface properties of other glass beads were modified by coating the glass beads with polyaerylic acid, [CH2CH(C00H)-]n. To accomplish the coating, the glass beads were immersed in the polyaerylic acid for 30 minutes and thereafter removed from the polyaerylic acid and dried. The sixth and seventh filter media material were tested for coagulant adsorption by the same approach as in Example 1. The results, expressed in the same manner as in Example 1, are: polyaerylic acid resin treated glass/Mayosperse 60, 1.2; polyaerylic acid treated glass/Mayosperse 60, 6.0. By comparison, the adsorption for untreated glass/Mayosperse 60 was 0.5. The surface treatment prior to adsorption was successful in both cases in increasing the absorption of the coagulant. All of the tested combinations achieved some degree of adsorption, with some much better than others. Other issues such as cost and durability may determine the choice of combinations of substrate material, possible pre-adsorption surface treatment, and coagulant in particular circumstances. Example 3 Studies of the operability of the present invention and comparative testing with the prior approaches were conducted using a laboratory-scale media filter formed of a four-inch diameter PVC pipe. Appropriate lines, valves, and pumps were provided. The system had the capability to operate with and without a continuous added flow of coagulant, to evaluate various operating conditions. The input fluid was municipal water, to which sufficient kaolin clay was added to provide a nominal turbidity of 1.5 NTU. Two coagulants were utilized in different test series, Filtermate 150 and Mayosperse 60, both described previously. In a first test series, a conventional mixed filter media material, termed a "mixed-media material", of 8 inches of crushed coal, 10 inches of sand, and 8 inches of garnet, with Filtermate 150 coagulant, was evaluated in three conditions. The results for percentage of colloidal solids removed are as follows: Table 1 Mixed Media Test Condition Pet Removed no coagulant used at all 75 (conventional filter) continuous addition of coagulant in optimum amount 95 adsorbed coagulant with no continuous flow of coagulant 85$ Example 4 The ion exchange resins were evaluated as candidates for use as the filter media material, using the test apparatus described in Example 3 and the same surface of resin for each test. The Dowex 51-XB resin was evaluated with (coated) and without (uncoated) the Filtermate 150 coagulant in the regenerated condition (sodium form) and the spent condition (calcium and magnesium form). No coagulant was added to the fluid flow in any of the tests. The results are as follows: Table 2 Test Condition Pet Removed spent/coated 89.1 regenerated/coated 73.6 spent/uncoated 75.3 regenerated/uncoated 69.2 The spent and coated resin produces the best results within this group. Example 5 Various combinations of filter media substrate, pretreatment, and media surface area were evaluated using the apparatus of Example 3. The media surface area was varied by varying the height of the amount of filter media material loaded into the column. The coagulant was Mayosperse 60 in each case. The results are as follows. In the table, "Coag." indicates whether a coagulant is adsorbed onto the surface of the particles, N being "no" and Y being "yes". Table 3 Area Filter Media Coag. Sq. Ft. Pct Removed 1. Coal N 110 64 2 . Mixed-]media N 540 75 3. Mixed-]media Y 540 85 4. Dowex N 760 77 5. Dowex Y 760 89 6. DP-1 Y 110 86 7. DP-1 Y 540 92 8. DP-1 N 1050 91 9. DP-1 Y 1050 96 10. Glass N 1010 89 11. . Glass Y 1010 90 12. Glass , polyac:rylic Y 1010 97 acid resin Pretreat Increasing amounts of any filter media increase the amount of colloids (i.e., turbidity) removed from the water. The adsorption of coagulant improved the performance of natural materials such as the mixed-media material , ion exchange resins such as the Dowex 51-XB resin, and glass. Glass beads that are not pretreated and have no adsorbed coagulant achieve 89 percent colloids removal, sample 10. If coagulant is adsorbed onto the glass beads, sample 11, the improvement is small. The glass beads of sample 12 are the sixth filter media material of Example 2, which were first pretreated with the polyaerylic acid resin prior to coagulant adsorption. The performance of these pretreated and adsorbed glass beads is the best attained with any of the filter media materials studied, achieving 97 percent colloids removal. Highly effective colloids removal can thus be achieved using inexpensive materials such as glass beads that have been pretreated prior to coagulant adsorption. Example 6 Removal of colloids from water with an excessively high turbidity was studied. The apparatus and approach of Example 3 were used, except that sufficient kaolin clay was added to achieve turbidity of 4.5 NTU. The filter media material was 1050 square feet surface area of DP-1 resin with Mayosperse 60 coagulant adsorbed. About 97.7 percent of the colloids were removed. The present invention thus improves the performance of media filtration systems.

Claims: CLAIMS What is claimed is: 1. A method of purifying a fluid flow, comprising the steps of: providing a stable, nontoxic coagulant compound in a form that can adsorb onto the surface of a filter media; providing a finely divided solid filter media that can adsorb the coagulant compound at its surface; treating the filter media with the coagulant compound form such that a quantity of the coagulant compound is adsorbed onto the surface of the filter media, in off-line treatment of the filter media; providing a flow of a fluid containing colloidal matter; and passing the fluid containing colloidal matter through the filter media, in on-line operation of the filter media. 2. A method of purifying a fluid flow, comprising the steps of: providing a coagulant compound in a form that can adsorb onto the surface of a filter media; providing a finely divided solid filter media that can adsorb the coagulant compound at its surface, the step of providing a finely divided solid filter media including the step of modifying the surface of the filter media to increase its ability to adsorb the coagulant compound at its surface; treating the filter media with the coagulant compound form such that a quantity of the coagulant compound is adsorbed onto the surface of the modified filter media, in off-line treatment of the filter media; providing a flow of a fluid containing colloidal matter; and passing the fluid containing colloidal matter through the filter media, in on-line operation of the filter media. 3. The method of claim 2, wherein the step of modifying includes the step of treating the surface of the filter media with a substance selected from the group consisting of acrylics, epoxies, phenolics, sulfonated plastics, polyurethanes , silanes, ion exchange resins, and nylons. 4. The method of claim 2, wherein the step of modifying includes the step of treating the surface of the filter media with polyaerylic acid. 5. The method of claim 2, wherein the step of modifying includes the step of contacting the surface of the finely divided filter media with a reactant that deposits an electronegative group on the surface of the filter media. 6. The method of claim 1 or claim 2, including the additional steps, after the step of passing, of removing the filter media from on-line operation; repeating the steps of providing a coagulant compound and treating the filter media; returning the filter media to on-line operation; and repeating the steps of providing a flow of a fluid and passing the fluid. 7. The method of claim 1 or claim 2 , including the additional steps, after the step of passing, of removing the filter media from on-line operation; backwashing the filter media In an off-line operation; returning the filter media to on-line operation; and repeating the steps of providing a flow of a fluid and passing the fluid. 8. The method of claim 1 or claim 2, wherein the step of providing a finely divided solid filter media includes the step of providing a filter media selected from the group consisting of acrylics, epoxies, phenolics, sulfonated plastics, polyurethanes, silanes, nylons, and ion exchange resins. 9. The method of claim 1 cr claim 2, wherein the step of providing a finely divided solid filter media includes the step of providing glass beads as the filter media. 10. The method of claim 1 or claim 2, wherein the step of providing a finely divided solid filter media includes the step of providing a filter media selected from the group consisting of silica-based materials, minerals, carbon-based materials, metals, ceramics, carbon-chain materials, filled plastics, and hollow, internally weighted plasti cs . 11. The method of claim 1 or claim 2, including the additional step, after the step of passing the fluid, of removing soluble impurities from the fluid flow. 12. The method of claim 1 or claim 2, wherein the step of providing a coagulant compound includes the step of providing a coagulant compound selected from the group consisting of a poly(diallyl-dimethyl ammonium chloride) coagulant, poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride, poly(2-hydroxy-propyl-N,N-dimethyl ammonium chlorides, quaternized polyamines, and polyamines other than melamine formaldehydes. 13. A method of preparing a filter media material, comprising the steps of: providing a stable, nontoxlc coagulant compound; providing a finely divided solid filter media that can adsorb the coagulant compound at its surface; treating the filter media with the coagulant compound form such that a quantity of the coagulant compound is adsorbed onto the surface of the filter media, and thereafter discontinuing the step of treating; and drying the filter media material.

Inventors: ANDERSON BRYCE P, COMSTOCK DANIEL L, DURHAM LEE A, WARREN MARK A, ANDERSON, BRYCE, P., COMSTOCK, DANIEL, L., DURHAM, LEE, A., WARREN, MARK, A.
Applicants: WALKER & ASS D W, D.W. WALKER & ASSOCIATES
Application year: 1994
Main classification: B01D37
IPC codes: B01D24, B01D37